Sample Preparation
The nutshells were cracked by a nutcracker and the kernels were isolated
from the shell. The shells were then segmented by Epilog Fusion M2 laser
cutter using CO2 laser and subsequently sanded to a
required uniform dimension. Sanding the cross-sectional areas also helps
to remove the laser-induced localized burned regions. The inner and
outer surface of the shells were also sanded partially to mitigate
uneven surface of the shell morphology. The samples obtain a
uniform form, making them suitable for application into numerous
practical devices. Samples were then cleaned with ultrapure water.
Nutshell samples were immersed in a solution consisting of 40% (v/v)
acetone, 30% (v/v) ethanol, and 30% (v/v) deionized (DI)
water. The mixture was heated at 70 °C for 20 minutes to break
the lignin and hemicellulose network. Samples were rinsed thoroughly
with ultra-pure water to eliminate the residues. Following the
treatments the samples were dried in a tube furnace at 100 °C for 1 h
under a constant flow of nitrogen gas. After being dried in the ambient
environment for 24 h, the samples are marked as Almond Shell - AS,
Filbert Shell - FS, Pecan Shell - PS, and Walnut Shell - WS. To enhance
the hydrophilicity, a few of the samples were further plasma cleaned for
8 minutes.